Preparation

Make the compote

• Combine the rhubarb, jam, sugar, lemon zest, and 1/4 cup water in a 3-quart saucepan. Bring to a boil over medium heat, then lower to a simmer. Continue to simmer, stirring frequently, until beginning to thicken, 5 to 7 minutes. Remove from the heat and let cool to room temperature. Thin with 3 Tbs. water, adding more in 1 Tbs. increments to reach your desired consistency.

Make the panna cottas

• Lightly spray six 6- to 8-oz. ramekins, small bowls, or pastry molds with cooking spray.
• Put the milk in a 2-quart saucepan and sprinkle with the gelatin. Allow the gelatin to soften for about 5 minutes. Place the saucepan over low heat and whisk in the sugar until the gelatin and sugar are completely dissolved, 2 to 3 minutes. Rub a little between your fingers to check. (Avoid simmering, which destroys the gelatin’s thickening ability; if you see bubbles, remove from the heat and let it cool.)
• Off the heat, whisk in the sour cream, vanilla and salt.
• Transfer the mixture to a large measuring cup and divide among the prepared ramekins. Cover loosely with plastic wrap. Refrigerate until set, 1 to 2 hours.
• 年代erve the panna cottas in their ramekins, or unmold: Moisten six serving plates with a little warm water (this makes it easier to center the panna cottas). Loosen the edges of a panna cotta with a fingertip, then slowly invert it onto a plate. Gently jiggle the ramekin side to side until the panna cotta slips out. Lift the ramekin, reposition the panna cotta on the plate, if needed, and pat the plate dry. Serve, chilled for a firm panna cotta or at room temperature for a softer one, with the sauce.

Make Ahead Tips

The compote can be covered and refrigerated for up to 5 days.

The panna cottas can be made 1 day ahead and refrigerated, covered.